Filter cartridges are used for a variety of jobs, e.g. the filtration of water, the filtration of air, the filtration of lubricants, etc. The filters with which the present invention is primarily concerned are those filters which are cylindrical in shape and which include a hollow cylindrical core the material surrounding the core can be radial pleats of filter material or other configurations of filter material. The filter material may be paper, plastic or metal. In some prior art filters, plastic webs are provided around the outside and around the core of the filter to add to the structural integrity of the assembly.
Such filter cartridges also typically include end caps for protecting and sealing the ends of the units. The end caps commonly include a flat annular surface adapted to abut the ends of the filter cartridge and a pair of annular collars. The first collar is centrally located and is adpated to fit within the core of the filter, while the second collar extends from the circumference of the flat surface to encircle the ends of the filter tube.
In the prior art, adhesives have been used to seal the end caps to the filter tube. Epoxies are frequently employed, but a wide variety of other sealants can be used as long as the adhesive is resistant to the fluid being filtered and to the temperatures encountered during use. Several problems have yet to be overcome in the use of such adhesives. The most troublesome problem to solve is the uniform application of adhesive. Because the filter medium is porous, it is essential that the ends be totally sealed to the end cap or else leaks will develop destroying the efficiency of the filter assembly. Another problem which has been encountered is the development of an efficient manufacturing process for properly sealing the end caps to the filter tube.
One prior art solution to the end cap sealing problem is suggested in Luchetta's U.S. Pat. No. 3,528,557 issued Sept. 15, 1974 for "Filter Construction." Luchetta relates the prior art problem of effective sealing to the uneven distribution of adhesives at the area between the ends of the pleats and the end cap. The solution suggested in Luchetta is to provide one or more annular ridges on the internal face of the end cap to separate the pleat ends slightly from the cap. The ridges are provided to reduce dry spots between the end caps and the pleats.
Another prior art patent showing the use of adhesives to seal a pleated paper element to a metal end cap is Mumby's U.S. Pat. No. 3,392,843 issued July 16, 1968 for "Pleated Filter Cartridge and Its Method of Manufacture." This patent merely discloses the use of a layer of liquid adhesive to seal the end caps to the paper. The adhesive is heated in an oven to affect the final seal.
The method for preparing filter cartridges which overcomes the above-noted disadvantages of the prior art would be a significant advance in this technology.